The keyed washer is already removed. You can see how the setup worked in the video, below, at about 2:02. The washer had an internal key that went into the slot you see in the steerer tube. So the washer wouldn't turn. The washer itself had a number of holes (one about every 10°) drilled into it. In the picture above you see a pin sticking out of the race. That pin would insert in one of the washer holes, preventing it from rotating.

You probably want to save the race (with pin intact!) and the washer and the fork. The standard ways are
1) penetrating oil like Kroil. If you don't care about the paint, a 50/50 mixture of ATF and acetone is said to work best.
2) If oil doesn't work, you could try heat. Heat the joint, carefully, with a torch (standard propane is probably fine). Easy does it.